fontmake fails with simple 5-master setup

I’ve been trying to turn these simple designspaces into a variable font, with no luck: [Archive.zip](https://github.com/googlei18n/fontmake/files/2225152/Archive.zip)

I get this output which I don’t really understand:

```
fontmake -m Test.designspace -o variable
INFO:fontmake.font_project:Building interpolation-compatible TTFs
INFO:ufo2ft:Pre-processing glyphs
INFO:cu2qu.ufo:New spline lengths:
INFO:ufo2ft.filters:Running DecomposeComponentsFilter on Unnamed-Regular
INFO:ufo2ft.filters:Running DecomposeComponentsFilter on Test-ThinExpanded
INFO:ufo2ft.filters:Running DecomposeComponentsFilter on Test-BlackExpanded
INFO:ufo2ft.filters:Running DecomposeComponentsFilter on Test-ThinCondensed
INFO:ufo2ft.filters:Running DecomposeComponentsFilter on Test-BlackCondensed
INFO:ufo2ft:Building OpenType tables for Unnamed-Regular
INFO:fontmake.font_project:Saving /var/folders/xl/xzdty8fj5db_9d8s_f6178m40000gn/T/ttf-interp-bznABA/Test-Regular.ttf
INFO:ufo2ft:Building OpenType tables for Test-ThinExpanded
INFO:fontmake.font_project:Saving /var/folders/xl/xzdty8fj5db_9d8s_f6178m40000gn/T/ttf-interp-bznABA/Test-ThinExpanded.ttf
INFO:ufo2ft:Building OpenType tables for Test-BlackExpanded
INFO:fontmake.font_project:Saving /var/folders/xl/xzdty8fj5db_9d8s_f6178m40000gn/T/ttf-interp-bznABA/Test-BlackExpanded.ttf
INFO:ufo2ft:Building OpenType tables for Test-ThinCondensed
INFO:fontmake.font_project:Saving /var/folders/xl/xzdty8fj5db_9d8s_f6178m40000gn/T/ttf-interp-bznABA/Test-ThinCondensed.ttf
INFO:ufo2ft:Building OpenType tables for Test-BlackCondensed
INFO:fontmake.font_project:Saving /var/folders/xl/xzdty8fj5db_9d8s_f6178m40000gn/T/ttf-interp-bznABA/Test-BlackCondensed.ttf
INFO:fontmake.font_project:Building variable font variable_ttf/Test-VF.ttf
INFO:fontTools.varLib:Axes:
OrderedDict([('weight', {u'map': None, 'name': 'weight', 'default': 400.0, 'tag': 'wght', 'maximum': 900.0, 'minimum': 100.0, 'labelname': {'en': 'Weight'}}), ('width', {u'map': None, 'name': 'width', 'default': 100.0, 'tag': 'wdth', 'maximum': 120.0, 'minimum': 75.0, 'labelname': {'en': 'Width'}})])
INFO:fontTools.varLib:Internal master locations:
[{'weight': 400.0, 'width': 100.0},
{'weight': 900.0, 'width': 75.0},
{'weight': 100.0, 'width': 120.0},
{'weight': 100.0, 'width': 75.0},
{'weight': 900.0, 'width': 120.0}]
INFO:fontTools.varLib:Internal axis supports:
{'weight': [100.0, 400.0, 900.0], 'width': [75.0, 100.0, 120.0]}
INFO:fontTools.varLib:Normalized master locations:
[{'weight': 0.0, 'width': 0.0},
{'weight': 1.0, 'width': -1.0},
{'weight': -1.0, 'width': 1.0},
{'weight': -1.0, 'width': -1.0},
{'weight': 1.0, 'width': 1.0}]
INFO:fontTools.varLib:Index of base master: 0
INFO:fontTools.varLib:Building variable font
INFO:fontTools.varLib:Loading master fonts
INFO:fontTools.varLib:Generating fvar
INFO:fontTools.varLib:Generating avar
INFO:fontTools.varLib:No need for avar
Traceback (most recent call last):
File "/Users/adam/Library/Python/2.7/bin/fontmake", line 11, in
sys.exit(main())
File "/Users/adam/Library/Python/2.7/lib/python/site-packages/fontmake/__main__.py", line 256, in main
project.run_from_designspace(designspace_path, **args)
File "/Users/adam/Library/Python/2.7/lib/python/site-packages/fontmake/font_project.py", line 623, in run_from_designspace
**kwargs)
File "/Users/adam/Library/Python/2.7/lib/python/site-packages/fontmake/font_project.py", line 689, in run_from_ufos
master_bin_dir=master_bin_dir)
File "/Users/adam/Library/Python/2.7/lib/python/site-packages/fontmake/font_project.py", line 259, in build_variable_font
font, _, _ = varLib.build(designspace_path, finder)
File "/Users/adam/Library/Python/2.7/lib/python/site-packages/fontTools/varLib/__init__.py", line 759, in build
model = models.VariationModel(normalized_master_locs, axisOrder=axisTags)
File "/Users/adam/Library/Python/2.7/lib/python/site-packages/fontTools/varLib/models.py", line 169, in __init__
self.locations = sorted(locations, key=keyFunc)
File "/Users/adam/Library/Python/2.7/lib/python/site-packages/fontTools/varLib/models.py", line 197, in key
onPointAxes = [axis for axis,value in loc.items() if value in axisPoints[axis]]
KeyError: 'wdth'
```